The Sign of Four

he Sign of Four was published in 1890 and is the second novel written by Conan Doyle to feature Sherlock Holmes. Conan Doyle wrote four novels and 56 short stories featuring this detective.

The story is set in 1888 and has a complex plot involving service in India, the Indian Rebellion of 1857, a stolen treasure and a secret pact among four convicts (the 'Four' of the title) and two corrupt prison guards. It presents the detective's drug habit and humanises him in a way that had not been done in the preceding novel, A Study in Scarlet. It also introduces Doctor Watson's future wife, Mary Morstan.

The Sign of Four was published in many editions: